Process for making a novel copper base alloy

ABSTRACT

A method of preparing a copper alloy is disclosed which comprises providing in the alloy about 0.8 - 2.3% iron and about 0.3 - 1.7% cobalt, such that the amount of iron plus cobalt ranges from about 1.5 - 2.5%, from about 5 - 13% zinc, balance essentially copper. The alloy is hot rolled at a temperature of at least 500*C, and cold rolled by a process which includes conducting at least one interanneal between successive cold reductions. The interanneal is conducted at temperatures ranging from about 400 to 600*C for a period of at least 15 minutes. Processing may also include a final anneal at a temperature of from 350 to 600*C conducted for at least 15 minutes. The novel alloy of this invention possesses a combination of strength and electrical conductivity which makes it a suitable replacement for the C.D.A. 400 series tin-brass alloys.

United States Patent [191 Crane et al.

[ 1 Dec. 3, 1974 1 PROCESS FOR MAKING A NOVEL COPPER BASE ALLOY [73]Assignee: Olin Corporation, New Haven,

Conn.

[22] Filed: Sept. 20, 1973 [21] Appl. No.: 399,073

Related U.S. Application Data [63] Continuation-impart of Ser. No.268,485, July 3,

1972, Pat. N0. 3,816,109.

[52] U.S. Cl 148/2, 148/l1.5 R, 148/l2.7, 148/32, 148/32.5 [51] Int. Cl.C22f l/08 [58] Field of Search 148/2, 3, 11.5 R, 12.7, 148/32, 32.5,13.2, 160; 75/153, 157.5

[56] References Cited UNlTED STATES PATENTS 1,723,922 8/1929 Corson 75153 1,959,509 5/1934 Tour....... 75/l57.5 2,126,827 8/1938 Smith148/ll.5 2,147,844 2/1939 Kelly 75/153 2,155,406 4/1939 Crampton75/157.5 X

2,169,188 8/1939 Kelly 75/157.5 X 2,295,180 9/1942 Mitchell 75/l57.5

Primary ExaminerC. Lovell Attorney, Agent, or Firm-David A. Jackson;Robert H. Bachman 5 7] ABSTRACT A method of preparing a copper alloy isdisclosed which comprises providing in the alloy about 0.8 2.3% iron andabout 0.3 1.7% cobalt, such that the amount of iron plus cobalt rangesfrom about 1.5 2.5%, from about 5 13% zinc, balance essentially copper.The alloy is hot rolled at a temperature of at least 500C, and coldrolled by a process which includes conducting at least one interannealbetween successive cold reductions. The interanneal is conducted attemperatures ranging from about 400 to 600C for a period of at least 15minutes. Processing may also include a final anneal at a temperature offrom 350 to 600C conducted for at least 15 minutes. The novel alloy ofthis invention possesses a combination of strength and electricalconductivity which makes it a suitable replacement for the C.D.A. 40,0series tin-brass alloys.

8 Claims, 11Drawing Figure PATENIEDBEB 31914 I l I A 700 200 300 400 500600 ROLLED ANA/EAL/A/G TEMPERATURE, c. (1 HOUR) PROCESS FOR MAKING ANOVEL COPPER BASE ALLOY CROSS REFERENCE TO RELATED APPLICATION Thepresent application is a continuation-in-part of copending applicationSer. No. 268,485, by Jacob Crane, Sam Friedman and Michael J. Pryor forCOP- PER BASE ALLOY, filed July 3, 1972, now US. Pat. No. 3,816,109.

BACKGROUND OF THE INVENTION This invention provides for the methods ofprocessing a copper base alloy disclosed in our co-pending applicationSer. No. 268,485. The novel alloys disclosed therein were found topossess a unique combination of strength and electrical conductivitywhich makes them suitable for use in structural electrical components.The alloy possesses sufficient ductility to be formed into intricateparts such as electrical receptacles. Since such parts are used in avariety of environments and are in a highly stressed condition, stresscorrosion is highly important.

Tin-brasses, namely, the C.D.A. 400 series alloys are commonly used forthis type of application since they combine the above describedproperties. In general, the electrical conductivity of these 400 seriesalloys ranges from 28% IACS for C.D.A. Alloy 425 which is the strongestof the series, to 41% IACS for C.D.A. Alloy 405 which possesses thelowest strength of the series. Various of these alloys, particularlythose containing higher tin concentrations, are difficult tomanufacture, particularly with regard to casting and hot rollability.

SUMMARY OF THE INVENTION In accordance with this invention, a copperbase alloy containing about 0.8 2.3% iron and about 0.3 1.7% cobaltwherein the amount of iron plus cobalt ranges from about 1.5 to 2.5%,from about 5 to 13% zinc, balance essentially copper, is prepared by aprocess which comprises hot rolling at a temperature of at least 500C,and cold rolling the alloy to a cross sectional area reduction of atleast 50%, said cold rolling including one or more cold reduction stepsfollowed by one or more interanneals conducted at a temperature of from400 to 600C for at least 15 minutes.

The novel alloys processed in accordance with this invention provideelectrical conductivity that is superior to those of the 400 seriestin-brasses at a comparable strength to limiting bend radius ratio; orat comparable conductivity, they provide superior strength to limitingbend radius ratio.

Accordingly, it is a principal object of this invention to provide amethod of processing a copper base alloy containing iron, cobalt andzinc within specific ranges which results in an alloy possessing animproved combination of strength and electrical conductivity.

It is a further object of this invention to provide a method asaforesaid which provides alloys with properties which make them suitablesubstitutes for the tinbrasses.

Other objects and advantages will become apparent to those skilled inthe art from the detailed description which follows.

BRIEF DESCRIPTION OF THE DRAWING The accompanying FIGURE is a graph oftensile strength (KS1) and electrical conductivity IACS) measured fromalloy samples annealed at various temperatures for 1 hour.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In accordance withthis invention, a method of processing a novel copper base alloy isdisclosed which achieves a unique combination of strength and electricalconductivity in the alloy that is superior to the tinbrasses, and isless difficult to practice.

The method of this invention initially comprises providing a copper basealloy containing from about 0.8 to about 2.3% iron and from about 0.3 toabout 1.7% cobalt such that the amount of iron plus cobalt ranges fromabout 1.5 to about 2.5%, from about 5 to about 13% zinc, balanceessentially copper. Impurities may be present in amounts which do notadversely affect the properties of the above alloy.

Impurities at the following levels separately or in combination do notadversely affect the casting or hot and cold rolling characteristics ofthe alloy. Thus, the alloy may contain up to about 0.03% phosphorous, upto about 0.03% lead, up to about 0.05% tin, up to about 0.05% nickel, uptoabout 0.10% manganese, up to about 0.10% aluminum, up to about 0.05%silver and up to about 0.10% silicon. It is preferred that the maximumtotal impurities be limited to less than 0.2% to minimize adverse affecton the properties of the alloys.

Melting and Casting: The copper is melted, the iron v and cobalt areadded to the melt and it is then heated to about 1300C and held at thattemperature until the iron and cobalt are thoroughly dissolved. Thetemperature of the melt is reduced to about 1200C and the zinc isthenadded. The temperature at which the molten alloy is poured should besufficiently high to assure a temperature no lower than about 1 C at themold, in order to avoid the formation of coarse primary particles richin iron and cobalt. Other casting parameters are in accordance withconventional practice in the art. The choice of casting method is notcritical, as the alloy can be either static cast or direct chill (DC)cast.

Hot Rolling: The case alloy is soaked at a temperature of from about 800to about 1000C and preferably from about 900 to about 950C. Soak time isnot critical and may be varied as desired from a few minutes up to anhour or more. The pass schedule may, likewise, be set as desired. Passspeed is variable, as reduction can be achieved in a matter of minutes,or could be extended to hours duration depending upon the particularsequence employed by the artisan. Thus, for example, reduction of fromSinches to 0.40 inches would take of the order of minutes if done at onetime, but could take hours if the alloy is permitted to cool off betweenpasses. Pass temperature, however, should preferably be above about 500Cbut below the melting temperature of the alloy. It would be possible topermit the alloy to cool below 500C between passes, however, suchpractice is uneconomical as extensive reheating would be necessary. ltis, therefore, preferable to maintain the alloy at a temperature above500C throughout the entire hot rolling step. The alloys of thisinvention have better than 75% cold rollability if the hot rollingoperation is completed above 500C. Finishing temperatures of lower than500C may be employed if some subsequent loss in cold rollability isacceptable.

Cold Rolling: The hot rolled alloy is then cold rolled. As previouslynoted, cold reductions in excess of 75% can be achieved if the hotrolling finishing temperature is above 500C. Cold rolling to anyspecified finished gage may require interannealing. After suitableannealing, the alloy still possesses cold rollability in excess of 75%reduction. Where the optimum combination of strength and formability ofa temper rolled product is desired, a minimum of 50% reduction should beattained prior to the last interanneal. Thus, if only one interanneal isemployed between two cold reductions, the alloy should be cold rolled toat least a 50% reduction in the first cold reduction, whereas if aseries of cold reductions and interanneals are employed, only the coldreduction conducted prior to the last interanneal must achieve therequired minimum of at least 50% reduction.

Annealing: Annealing for softening can be performed either by bell orstrip annealing. The choice of bell annealing versus strip annealing ispredicated upon desired electrical conductivity. Where maximumconductivity is required, bell annealing is preferred.

As noted earlier, for the purpose of obtaining improved strength in thecold worked condition, at least one interanneal is conducted betweensuccessive cold reductions. The interanneal should be carried out for aperiod of at least minutes at temperatures of from about 400 to about600C. Preferably the interanneal is conducted at a temperature rangingfrom about 450 to about 550C for from about 1 to about 16 hours. It hasbeen found that this latter schedule yields more favorable results whenbell annealing is conducted. At least one interanneal is required toachieve a strength potential within the scope of this invention,however,

multiple interanneals can be used between cold reductions as desired. 1

\ It has been observed that the alloy prepared by this process possessesan unexpectedly improved strength and conductivity over alloys preparedby a process which employs only cold reduction. These findings areillustrated by the results of Example I which follows.

EXAMPLE I An alloy was prepared having the following composition (inweight percent): Cu 11.3% Zn 1.6% Fe 0.5% Co. The alloy was melted at1300C and DC cast at 1 190C. The cast alloy was hot rolled from 5 inchesthick to 0.40 inch thick at a starting temperature of 960C and afinishing temperature of 690C, and was then coil milled to 0.360 inchthick to produce a clean surface. The hot rolled plate was thenprocessed variously as follows:

PROCESS A:

cold rolled 60% PROCESS 8:

cold rolled 77% PROCESS C:

TABLE I UTS Number of In- Process Final Reduction (KSl) Process AnnealsA 60 83 None B '77 88 None C 50 .91 l D 6t 96 l E 50 90 2 F 98 2Referring to the results of Table I, it is noted that the alloy preparedby Process D, in accordance with this invention, which involved 61% coldreduction and one interanneal, possessed an ultimate tensile strength of96 KS1, whereas the same alloy prepared by Process A, which involved a60% cold reduction but which omitted the interannealing step, possessedan ultimate tensile strength of only 83 KSI. Likewise, the alloyprepared by Process F which involved a 75% cold reduction and twointeranneals, possessed an ultimate tensile strength of 98 KSI, whereasthe same alloy prepared by Process B, which involved a 77% coldreduction with no interannealspossessed an ultimate tensile strength of88 KS1. It is clear from this comparison that the employment of at leastone interanneal provides a significant improvement in the tensilestrength of the cold rolled alloys which cannot be duplicated simply byincreased cold reduction only.

It has also been found that the bend properties of an alloy at a givenstrength level are affected by the interannealing parameters employed.Thus, variation of either one or both of the temperature and duration ofthe interanneal can result in alloys which have different minimum bendradii. This relationship is illustrated in Example ll, below.

EXAMPLE II Two alloys of composition (in weight percent) Cu [2.2% Zn1.7% Fe 0.6% Co, and Cu l0.0% Zn 1.7% Fe 0.5% Co, respectively, weremelted at l300C and Durville cast at 1175C. The alloys were hot rolledfrom 1 inches thick to approximately 0.35 inch thick at startingtemperatures of about 950C and a finishing temperature of about 625C;surface milled to produce a clear surface; cold rolled to 0.080 inchgage; annealed at various temperatures for various times; cold rolled to0.020 inch gage.

The tensile strength and minimum bend radius of the 0.020 inch gagemetal measured with the bend axis parallel to the rolling direction (badway bend), and 90 to the rolling direction good way bend) are shown inTable 11, below.

31% IACS. Thus, as shown in the FIGURE, the preparation of a finallyannealed alloy possessing a particular combination of tensile strengthand conductivity can be controlled by the careful selection of the finalannealing temperature.

' Referring again to the FIGURE, the strength and conductivity of theas-rolled alloy were also measured For final gage annealing of coldmetal, a range of about 350 to about 600C is desirable. The annealingtemperature within this range may be varied depending upon the strengthand electrical conductivity properties desired in the alloy. Thus, formaximum conductivity, annealing is preferably conducted in the range ofabout 350 to about 450C, whereas if major softening is desired,annealing in the range of about 400 to about 600C is preferred. Finalgage annealing is normally conducted for at least minutes, and ispreferably conducted for a period of from about I to about 8 hours. Theemployment of the final gage anneal in the above-described manner isillustrated in Example 111, below.

EXAMPLE 111 An alloy of composition Cu 1 1.9% Zn 1.5% Fe 0.5% Co wasmelted at 1300C and DC cast at 1 175C. The alloy was then hot rolledfrom 3 inches thick to approximately 0.40 inch thick at a startingtemperature of 975C and a finishing temperature of about 400C. The

hot rolled alloy was then surface milled to product a clean surface;cold rolled to 0.080 inch gage; annealed at 500C for 1 hour; and coldrolled to 0.020 inch final gage. The samples thus prepared were thenfinally annealed at various temperatures for 1 hour.

The electrical conductivities and tensile strengths of the variouslyannealed samples were measured, and the resulting data is presented inthe graph in the accompanying FIGURE, wherein electrical conductivityand tensile strength have been plotted as functions of annealingtemperature.

Referring to the FIGURE, it can be seen that, in the range of 350 450C,an optimum combination of strength and conductivity is attained thatresults in alloys suited for a wide variety of electrical uses. Also, asstated earlier, temperatures of between 350 and 450C yield maximumconductivity, as conductivities of between about 35 to about 37% IACSare shown. Likewise, if further softening is desirable, temperaturesranging from 400 to 600C could be employed with only a minor loss ofconductivity, i.e. levels of 33 to and plotted. The resulting datademonstrates that high tensile strength and acceptable conductivity areattainable by the employment of an interannealing step during the coldrolling of the alloy, in accordance with the process of this invention.

When cast in accordance with the methods of this invention, the copperalloy possesses a microstructure characterized by an average graindiameter in the order of 0.1 mm and an iron-cobalt rich phase with aparticle size in the order of 0.01 mm, more or less uniformly Vdistributed throughout the copper matrix. The said particles tend tohave angular boundaries, with the exception of some particles which mayexhibit dendritic form with short dentrite arms.

The microstructure resulting from annealing the cold worked metal in thetemperature range of about 450 to about 650C is characterized by fine,equiaxed grains which resist significant growth. The averagerecrystallized grain diameter remains less than 0.010 mm in diameterover the aforementioned temperature range. The approximate equiaxediron-cobalt rich particles that exist in the cast structure, areelongated in the rolling direction, the extent of the elongation beingdependent upon the total percent reduction of the main body of metal. x

The alloys prepared by the process of this invention have particularapplication in structural electrical components such as electricalcontacts, electrical receptacles, electrical connectors and the like.

All of the compositions specified in this application by percentage aregiven in percentage by weight.

This invention may be employed in other forms or carried out in otherways without departing from the spirit or .essential characteristicsthereof. The present embodiment is therefore to be considered as in allrespects illustrative and not restrictive, the scope of the inventionbeing indicated by the appended claims, and all changes which comewithin the meaning and range of equivalency are intended to be embracedtherein.

What is claimed is:

l. A method of preparing copper alloys consisting essentially of about0.82.3% iron and about 0.3-1.7%

cobalt, such that the amount of iron plus cobalt ranges from about l .5to 2.5%, from to l3% zinc and the balance essentially copper, to provideimproved strength, bend properties, and electrical properties whichcomprises:

a. hot rolling the alloy at a temperature of at least 500C. but belowits melting temperature; and

b. cold rolling to at least 50% cold reduction wherein said cold rollingincludes successive cold reductions and at least one interannealconducted there between at temperatures ranging from about 400 to 600Cfor a period of at least minutes.

2. The method of claim 1 wherein the cold reduction conducted prior tothe last interanneal yields a cross sectional area reduction of at least50%.

3. The method of claim 1 wherein said interanneal is conducted attemperatures ranging from about 450 to 500C for from l to 4 hours 4. Themethod of claim 1 wherein said alloy is melted at a temperature of fromabout 1200 to l300C, and cast at a temperature such that the resultantmold temperature is at least 1 175C.

5. The method of claim I wherein, prior to hot rolling, the alloy issoaked at a temperature of from 800 to l000C for a period of up to 1hour.

6. The method of claim 5 wherein said alloy is soaked at a temperatureof from 900 to 950C.

7. The method of claim 1 wherein the cold rolled alloy is finallyannealed at a temperature of 350 600C for at least 15 minutes.

8. The method of claim 7 wherein the final anneal is conducted at atemperature of from 350 to 450C for from 1 to 8 hours.

RUTH C. MASON "UNITED STATES PATENT OFFICE I CERTIFECATE OF CORRECTIONPatent No. 3,852,121 Dated December 3, 197

Inventor(s) Jacob Crane, Sam Friedman and Michael J. Pryor It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

In Colume 8', corresponding to Claim 3, line 1, after "to", pleasedelete the number "500C" and insert in its place 550C signed and sealedthis 11th day of March- 1975.

(SEAL) Attest:

C. MARSHALL DANN Commissioner of Patents Attesting Officer and'Trademarks

1. A METHOD OF PREPARING COPPER ALLOYS CONSISTIG ESSENTIALLY OF ABOUT0.8-2.3% IRON AND ABOUT 0.3-1.7% COBALT, SUCH THAT THE AMOUNT OF IRONPLUS COBALT RANGES FROM ABOUT 1.5 TO 2.5%, FROM 5 TO 13% ZINC AND THEBALANCE ESSENTIALLY COPPER, TO PROVIDE IMPROVED STRENGTH, BENDPROPERTIES, AND ELECTRICAL PROPERTIES WHICH COMPRISES: A. HOT ROLLINGTHE ALLOY AT A TEMPERATURE OF AT LEAST 500*C, BUT BELOW ITS MELTINGTEMPERATURE; AND B. COLD ROLLING TO AT LEAST 505 COLD REDUCTION WHEREINSAID COLD ROLLING INCLUDES SUCCESSIVE COLD REDUCTIONS AND AT LEAST ONEINTERNNEAL CONDUCTED THEREBETWEEN AT TEMPERATURES RANGING FROM ABOUT 400TO 600*C FOR A PERIOD OF AT LEAST 15 MINUTES.
 2. The method of claim 1wherein the cold reduction conducted prior to the last interannealyields a cross sectional area reduction of at least 50%.
 3. The methodof claim 1 wherein said interanneal is conducted at temperatures rangingfrom about 450 to 500*C for from 1 to 4 hours.
 4. The method of claim 1wherein said alloy is melted at a temperature of from about 1200 to1300*C, and cast at a temperature such that the resultant moldtemperature is at least 1175*C.
 5. The method of claim 1 wherein, priorto hot rolling, the alloy is soaked at a temperature of from 800 to1000*C for a period of up to 1 hour.
 6. The method of claim 5 whereinsaid alloy is soaked at a temperature of from 900 to 950*C.
 7. Themethod of claim 1 wherein the cold rolled alloy is finally annealed at atemperature of 350 - 600*C for at least 15 minutes.
 8. The method ofclaim 7 wherein the final anneal is conducted at a temperature of from350 to 450*C for from 1 to 8 hours.